Microarrays and nanoarrays are important commercial developments. The use of microarrayed-patterned biomolecules, such as DNA, proteins, and cells, has led to extensive and significant advances in fields such as geonomics and proteomics, with applications to many areas of medical and biological research; see for example Miller, et al., Microarray Technology and Its Applications; Springer; N.Y. (2005). Within current microarray technology, a need exists to decrease spot-size to the nanometer regime, thus increasing the density of combinatorial libraries. This can not only increase the number of interactions one can simultaneously monitor, but also decrease the amount of costly reagents necessary for example to sequence an organism's DNA or screen interactions. With the advent of powerful new nanolithographic methods, such as dip-pen nanolithography (DPN) printing or patterning (see for example Piner et al., Science, 283, 661-663 (1999)), there is now the ability to reduce the feature size in such 1-dimensional or 2-dimensional arrays to their physical limit, the size of the structures from which they are made of and the size of the structures they are intended to interrogate; see for example Rosi et al., Nanostructures Chemical Reviews, 105, 1547-1562 (2005). Such massive miniaturization not only allows one to increase the density of combinatorial libraries, increase the sensitivity of such structures in the context of a biodiagnostic event, and reduce the required sample analyte volume, but also allows one to carryout studies not possible with the more conventional microarray format.
In order to achieve the potential DPN may offer to the field of patterned biomolecule arrays, simple and/or robust techniques can be developed for the direct-write patterning of biomolecules at the nanometer scale. Also, massively parallel, multiplexed patterning of biomolecules is desirable. Conventional methods of biomolecule patterning by DPN are generally limited to a single ink composition, be it oligonucleotide or protein. Multiple-ink DPN patterns require first patterning a single component biomolecule, then performing a lengthy alignment procedure before patterning a second biomolecule. One prominent technical challenge in creating multiplexed biomolecule patterns deposited in a massively parallel format resulting from the different diffusion rates inherently associated with different biomolecules; see for example Lee et al., J. Am. Chem. Soc. 125, 5588-5589 (2003); Lim et al., Angew. Chem. Int. Ed. 42, 2309-2312 (2003). Previous advances in this area have been made, but needs yet exist, particularly for commercial applications. One potential limitation is the chemical modification of a tip such as an AFM tip for reproducible tip coating. Different biomolecules may require a specific modification, which can lead to compatibility issues. The second is in the context of parallel DPN printing. Biological molecules can have different transport properties, which can lead to heterogeneous surface features from tip-to-tip, and in some cases, cannot be deposited at all. Finally, denaturation and loss of biological activity potentially can be an issue. In order to bypass these potential limitations, a method that can equalize the transport rates while preserving the biological activity of the molecules is desirable.